HTTP/1.1 200 OK Date: Mon, 08 Apr 2002 23:46:25 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Wed, 30 Jul 1997 11:13:00 GMT ETag: "2e98ea-236f-33df21bc" Accept-Ranges: bytes Content-Length: 9071 Connection: close Content-Type: text/plain Network Working Group Greg Vaudreuil Internet Draft Octel Communications Expires in six months Glenn Parsons Obsoletes: RFC 1911 Nortel Technology July 29, 1997 Toll Quality Voice - 32 kbit/s ADPCM MIME Sub-type Registration Status of this Memo This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet Drafts as reference material or to cite them other than as a "work in progress". To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Overview This document describes the registration of the MIME sub-type audio/32KADPCM for toll quality audio. This audio encoding is defined by the ITU-T in Recommendation G.726. Internet Draft 32 kbit/s ADPCM July 29, 1997 1. Abstract This document describes the registration of the MIME sub-type audio/32KADPCM for toll quality audio. This audio encoding is defined by the ITU-T in Recommendation G.726. This document refines an earlier sub-type registration in RFC 1911. 2. ITU-T Definition Recommendation G.726 [G726] defines the characteristics that are recommended for the conversion of a 64 kbit/s A-law or m-law pulse code modulation (PCM) channel at 8000 samples/second to and from a 40, 32, 24 or 16 kbit/s channel. The conversion is applied to the PCM bit stream using an adaptive differential pulse code modulation (ADPCM) transcoding technique. This Recommendation obsoletes G.721 which only defined the 32 kbit/s characteristics. Recommendation G.726 was prepared by Study Group 15 of the Telecommunications Standardization Sector of the International Telecommunication Union (ITU-T) and was approved under the ITU's Resolution No. 2 procedure on the 14 of December 1990. 3. MIME Definition 3.1 audio/32KADPCM CCITT Recommendation G.726 [G726] describes the algorithm recommended for conversion of a 64 kbit/s A-law or u-law PCM channel to and from a 32 kbit/s channel (this is the same algorithm as described in the deprecated G.721). The conversion is applied to the PCM stream using an Adaptive Differential Pulse Code Modulation (ADPCM) transcoding technique. The MIME sub-type audio/32KADPCM is defined to hold binary audio data encoded in 32 kbit/s ADPCM exactly as defined by ITU-T Recommendation G.726. No header information shall be included as part of the audio data. The content transfer encoding is typically either binary or base64. An additional consideration that this document defines for clarity is the choice of little endian ordering of the four bit code words. This default ordering is defined in ITU-T Recommendation X.420 [X420] for the equivalent X.400 body part, but is also detailed below in the IANA Registration. 3.2 VPIM Usage Vaudreuil, Parsons Expires 01/29/98 [Page 2] Internet Draft 32 kbit/s ADPCM July 29, 1997 The audio/32KADPCM sub-type is a primary component of the VPIM specification [VPIM]. In this context, the Content-Description and Content-Disposition headers are used to succinctly describe the contents of the audio body. As well, only the little endian bit ordering is valid. Refer to the VPIM Specifcation for proper usage. 4. IANA Registration To: ietf-types@iana.org Subject: Registration of MIME media type audio/32KADPCM MIME media type name: audio MIME subtype name: 32KADPCM Required parameters: none Optional parameters: none Encoding considerations: Binary or Base-64 generally preferred Security considerations: none Interoperability considerations: The four bit code word ordering within a byte may differ between existing implementations of G.726 codecs. Since this content only permits the little endian ordering, codecs that support the opposite ordering must reorder the code words before storing to or retrieving from this content type. Published specification: ITU-T G.726 with little endian ordering Applications which use this media type: primarily voice messaging Additional information: Magic number(s): ? File extension(s): .721 Macintosh File Type Code(s): APCM Little Endian Ordering: Vaudreuil, Parsons Expires 01/29/98 [Page 3] Internet Draft 32 kbit/s ADPCM July 29, 1997 The 4-bit code words of the G.726 encoding MUST be packed into octets/bytes as follows: the first code word (A) is placed in the four least significant bits of the first octet, with the least significant bit (LSB) of the code word (A1) in the least significant bit of the octet; the second code word (B) is placed in the four most significant bits of the first octet, with the most significant bit (MSB) of the code word (B4) in the most significant bit of the octet. Subsequent pairs of the code words shall be packed in the same way into successive octets, with the first code word of each pair placed in the least significant four bits of the octet. It is preferred that the voice sample be extended with silence such that the encoded value comprises an even number of code words. However, if the voice sample comprises an odd number of code words, then the last code word shall be discarded. +--+--+--+--+--+--+--+--+ |A1|A2|A3|A4|B1|B2|B3|B4| +--+--+--+--+--+--+--+--+ LSB -> | 0| 1| 2| 3| 4| 5| 6| 7| <- MSB +--+--+--+--+--+--+--+--+ 32K ADPCM / Octet Mapping Person & email address to contact for further information: Glenn W. Parsons Glenn.Parsons@Nortel.ca Gregory M. Vaudreuil Greg.Vaudreuil@Octel.Com Intended usage: COMMON Author/Change controller: Glenn W. Parsons & Gregory M. Vaudreuil 5. Authors' Addresses Glenn W. Parsons Nortel Technology P.O. Box 3511, Station C Ottawa, ON K1Y 4H7 Canada Phone: +1-613-763-7582 Fax: +1-613-763-8385 Glenn.Parsons@Nortel.ca Vaudreuil, Parsons Expires 01/29/98 [Page 4] Internet Draft 32 kbit/s ADPCM July 29, 1997 Gregory M. Vaudreuil Octel Communications 17080 Dallas Parkway Dallas, TX 75248-1905 United States Phone/Fax: +1-972-733-2722 Greg.Vaudreuil@Octel.Com 6. References [G726] CCITT Recommendation G.726 (1990), General Aspects of Digital Transmission Systems, Terminal Equipment - 40, 32, 24,16 kbit/s Adaptive Differential Pulse Code Modulation (ADPCM). [MIME4] N. Freed and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures", RFC 2048, Innosoft, First Virtual, Nov 1996. [VPIM1] Vaudreuil, Greg, "Voice Profile for Internet Mail", RFC 1911, Feb 1996. [VPIM2] Greg Vaudreuil and Glenn Parsons, "Voice Profile for Internet Mail - version 2", Work in Progress, July 1997. [X420] ITU-T Recommendation X.420 (1996) - ISO/IEC 10021-7:1996, Message handling systems: Interpersonal messaging. Vaudreuil, Parsons Expires 01/29/98 [Page 5]